perf hists browser: Move coloring logic to hpp functions

Move coloring logic into the hpp functions so that each value can
be colored independently.  It'd required for event group view.

For overhead column, add a callback for printing 'folded_sign' of
callchains of a hist entry.

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1358845787-1350-11-git-send-email-namhyung@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>